RBSE Class 10 Science Solutions Chapter 9 Heredity and Evolution
RBSE Class 10 Science Solutions Chapter 9 Heredity and Evolution
RBSE Class 10 Science Chapter 9 Heredity and Evolution InText Questions and Answers
Page 143.
Question 1.
If a trait ‘A’ exists in 10% of a population of an asexually reproducing species and a trait ‘B’ exists in 60% of the same population, which trait is likely to have arisen earlier?
Answer:
Symtoms in asexually producing organisms are transferred from one generation to other without differentiation therefore, ‘trait – B’ has arisen earlier because it is found in 60% organisms while ‘trait – A’ present only in 10% members of population. So ‘trait – B’ arisen earlier.
Question 2.
How does the creation of variation in a species promote survival ?
Answer:
Development of variations increases the survivability of species because due to variations useful changes come in plants and animals and variation helps adopt the animal in changed environment. For example, bacteria that can withstand heat will survive better in a heat wave. Variations with the existence of animal also make better for struggle. So variations are the basis of evolution.
Page 147.
Question 1.
How do Mendel’s experiments show that traits may be dominant or recessive?
Answer:
Mendel selected two alternative plants of pea for his experiment, like tall plants of pea, which only produced the tall plants of pea and dwarf plants of pea, which only produced the dwarf plants of pea. When Mendel crossed these two plants in F1? all plants were tall. By this it was clear that the tallness character (TT) was dominant over the dwarfness character (tt) and tallness charactef was hidden due to recessive character.
When Mendel performed the self-pollination in the F1 generation plants and by this the obtained seeds were grown then in F2 generation both characters would be obtained i’e. tall plants as well as dwarf plants (in the ratio of 3 : 1). It means tall character is dominant and dwarf character is
On the basis of this description or experiment establishment of first law of ‘Mendel Law of dominance’.
Question 2.
How do Mendel’s experiments show that traits are inherited independently?
Answer:
Mendel selected the two pairs of contrasting character for his experiments, like yellow, round and green, wrinkled seed plants. When Mendel crossed the yellow, round seed plants to green, wrinkled seed plants, then in F1generation all plants obtained were yellow round (RrYy).
When he allowed F1generation plants for self-pollination, then in F2 generation four types plant were obtained:
- 9 plants having the round and yellow seeds.
- 3 plants having the wrinkled and yellow seeds.
- 3 plants having the round and green seeds.
- 1 plant having the wrinkled and green seed.
In this way the phenotype of plants innu dihybrid cross of F2 generation is 9 : 3 : 3 :
1. This is called dihybrid ratio, we can understands this in the following way:
| Ratio | |
| 1. 315 Round. yellow seed | 9 |
| 2. 108 Round, green seed | 3 |
| 3. 101 Wrinkled, yellow seed | 3 |
| 4. 32 Wrinkled, green seed | 1 |
| 5. 556 seed 16 | 16 |
By means of this experiment it is clear that inheritance of shape and colour of seeds is not effected by one another. These characters inherited independently. So it is called Mendel’s law of independent assortment.
Question 3.
A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the Etraits – blood group A or O-is dominant? Why or why not?
Answer:
This information is not sufficient to tell which of the blood groups ‘A’ or ‘O’ is dominant. Blood group ‘A’ is always dominant in ABO blood group whereas blood group ‘O’ is recessive. Therefore, here the gene for, father’s blood group can be ‘AA’ (homozygous) or ‘AO’ (heterozygous), whereas the gene for mothers blood group can be ‘AO’ or ‘OO’.
Question 4.
How is the sex of the child determined in human beings?
Answer:
Sex chromosome present in man determines the sex of child. Determination of sex in child of human takes place in the following procedure:
- In man both sex chromosomes are different. In these one is X other is Y i.e., in man sex chromosomes are XY.
- In woman both sex chromosomes are similar i.e. XX.
- Man develops two types of sperms. Half sperms consists X chromosome while remaining lf half of sperms contain Y chromosomes.
- Woman develops only one type of egg (ovum), which consists of X chromosome.
- When X containing sperm fuse with X egg, developing child is girl (XX).
- When Y chromosome containing sperm fuse with X egg. developing child is boy (XY).
- In this way sperms of male are responsible for sex determination of child.
Page 150.
Question 1.
What are the different ways in which individuals with a particular trait may increase in a population?
Answer:
The following ways by which individuals with a particular trait may increase in a population:
(1) Natural selection
(2) Genetic Drift
(3) Food.
Question 2.
Why are traits acquired during the life-time of an individual not inherited?
Answer:
The effect of an acquired traits only on somatic cells. It does not effect on genetical material DNA. Because changes in genetical material can inherit in next generation. So acquired traits usually are not inherited in next generation.
Question 3.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer:
The small numbers of tigers is a matter of worry from the point of view of the genetics because their numbers are continuously decreasing. It shows that tigers are lagging behind, in natural selection i.e. in them no changes are taking place favourable to nature, by which their number can increase. Set of genes are also limited in their population. During sexual reproduction the variations in their character is also limited. So in changing conditions, their survival can be difficult.
Page 151.
Question 1.
What factors could lead to the rise of a new species?
Answer:
In origin of new species the following factors are helpful:
- Natural selection.
- Genetical drift.
- Geographical isolation of two sub – populations. Due to this members of population will be incapable of reproducing with each other.
- Variations developed by sexual reproduction i.e. germinal isolation.
Question 2.
Will geographical isolation be a major factor in the speciation of a self pollinating plant species? Why or why not?
Answer:
Geographical isolation can not be the reason of speciation in self pollinated plants because no entrance of new gene and not the formation of new species. In this way there may be the chances of coming some variations.
Question 3.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer:
Geographical isolation can not be a major factor in the speciation of an asexually reproducing organisms because in asexual reproduction only one cell takes part so there is neither genetic drift and nor gene flow.
Page 156.
Question 1.
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer:
The basic structure of forelimbs of frog, lizard, birds and horse are similar and bones present in forelimbs are also similar while they belong to different species. But the functions of forelimbs are different in above animals. So by this it is proved that the origin of these species is from one. ancestor and they show similarity although they belong to different species, it decides the evolutionary relation of two species.
Question 2.
Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Answer:
Such organs whose basic structure and origin is similar, but functions are different are called homologous organs. Because the functions of fin in bat and butterfly is similar (fly) but there origin and basic structure are different. So they are not homologous organs.
Question3.
What are fossils? What do they tell us about the process of evolution?
Answer:
Fossil Remains of the organisms of the remote past preserved in rocks of earth are called fossils. The age of these is decided with the help of radioisotopes material. They show the following matter about the evolution:
- Fossils give information about extinct organisms and also explain how evolution has occurred.
- Fossils can be used to determine the evolutionary history of an organism.
- The distribution of fossils at different levels of the ground gives information about which organism originated in which period and went extinct.
- Many fossils are helpful in understanding the evolutionary relationship between two different classes of organisms as joining link between then.
Page 158.
Question 1.
Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?
Answer:
The differences in size, shape and colour type etc. in human is due to the changes in its physical characters by the factors of geographical environment. But geographical environmental changes do not effect to its characteristics of biological structure. So no change comes on its body organs, but due to changes in geographical conditions clearly seen the change in its size, shape, colour etc. while they are the member of single species ‘Homo Sapiens’.
Question 2.
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Answer:
In evolutionary terms, it is not possible to tell that which among bacteria, spiders, fish and chimpanzees have a better body design because the physical development of these organisms is based on the need of survival and not on the basis of excellence. For example: as the powerful arms of a chimpanzee make it capable of many actions, whereas the bacteria can survive in such odd conditions where it is not possible for other organisms to survive.
RBSE Class 10 Science Chapter 9 Heredity and Evolution Textbook Questions and Answers
Question 1.
A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as:
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Answer:
(c) TtWW
Question 2.
An example of homologous organs is:
(a) our arm and a dog’s fore – leg.
(b) our teeth and an elephant’s tusks.
(c) potato and runners of grass.
(d) all of the above.
Answer:
(d) all of the above.
Question 3.
In evolutionary terms, we have more in common with:
(a) a Chinese school – boy ’
(b) a chimpanzee
(c) a spider
(d) a bacterium
Answer:
(a) a Chinese school-boy
Question 4.
A study found that children with light – coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Answer:
The children of parents (mother- father) with light coloured eyes also have light coloured eyes. On the basis of this the trait of light colour eye is dominant or recessive. Because if the genetype for light coloured eyes in parents is homozygous dominant or heterozygous recessive, then in both the conditions the child will have light coloured eyes.
Question 5.
How are the areas of study- evolution and classification-interlinked?
Answer:
The more characteristics two species will have in common, the more closely they are related. And the more closely they are related, the more recently they will have had a common ancestor. For example: a brother and a sister are closely related. They have common ancestors in the first generation before them, namely, their parents. A girl and her first cousin are also related, but less than the girl and her brother. This is because cousins have common ancestors, their grandparents, in the second generation before them, not in the first one. We can now appreciate that classification of species is in fact a reflection of their evolutionary relationship.
Question 6.
Explain the terms analogous and homologous organs with examples.
Answer:
Homologous Organs:
Those organs which have the similar basic structure and origin but are different in functions are known as homologous organs. For example, forelimbs of whale, bird, bat, horse and human being are homologous organs. External appearance of forelimbs are different in these animals. Their external forms are favourable to habit and habitat. Forelimbs of whale is flipper for swimming, forelimbs of bird and bat modified into feathers for flying, while forelimb of horse for running and free hand of human is suitable for catching.
The function and external structure of the forelimbs are unsimilar in these animals but the basic structure and origin is similar in all these animals. Such organs are called homologous organs. The homologosity of these organs are proved that all these animals have evolved from common ancestors and in past period they successively evolved.
Analogous Organs:
The organs which have the same function but there is the difference in basic structure and origin, are called analogous organs. For example, wings of insect, birds and bats are having the function in flying but there is a-lot of difference in origin and basic structure. In these organs only pseudo similarities are found due to habit and environment their functions are similar. Development of feathers in insects is in the form of protuberance comes out from the wall of the body while in birds and bats their origin is not from the protuberance of wall of the body. So there are the similarity in function but difference in origin and structure.
Question 7.
Outline a project which aims to find the dominant coat colour in dogs.
Answer:
Firstly make a survey in nearby area and find the population of dogs.
- After this find the percentage of different skin colours of dogs.
- Now find out such dogs in which colour of parents dogs and bitch skin colour is the same.
- Now make cross in dogs having the different colour of skin, like
A cross was done between a male dog having black colour and homozygous to a female dog having white colour and homozygous. In generation all dogs are having the black colour. It means the black colour of skin is dominant. We can show to this in the following way
So in F2 generation 3 black colour and 1 white colour dog is obtained, which shows that black colour is dominant over white colour.
Question 8.
Explain the importance of fossils in determining evolutionary relationships.
Answer:
Importance of fossils in establishing the evolutionary relationship:
(i) Fossils prove that from very old period (ancient time) the evolution is going on. Upto now only we have obtained the com¬plete series of evolution of horse, elephant and human.
(ii) Age of fossils is also determined by which we can get the knowledge of that time, when they were active.
(iii) By its impression or on the basis of fossil, we can develop complete picture with imagination.
(iv) The fossils of archaeopetryx obtained from 15 million old Jurassic rocks approximately. It is a connecting link between reptiles and birds. These were long tail, teeth in beak and claws on fingers of forelimb like reptiles but even then it was a bird because its forelimbs were modified into wings for fly. So it is clear and gives an evidence that birds originated from reptiles.
Question 9.
What evidence do we have for the origin of life from inanimate matter?
Answer:
J.B.S. Haldane, a British scientist (who became a citizen of India later), suggested in 1929 that life must have developed from the simple inorganic molecules which were present on earth soon after it was formed. He speculated that the conditions on earth at that time, which were far from the conditions we see today, could have given rise to more complex organic molecules that were necessary for life. The first primitive organisms would arise from further chemical synthesis.
Stanley L. Miller and Harold C. Urey in 1953, -they assembled an atmosphere similar to that thought to exist on early earth. This had molecules like ammonia, methane and hydrogen sulphide, but no oxygen. In one container there was water. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning. At the end of a week, 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules. So we can say that the origin of life arise from non living materials.
Question 10.
Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
Answer:
Sexual reproduction gives rise to more viable variations than asexual reproduction. Asexual reproduction takes place in single individual due to this only the same characters passes to its progeny. But in sexual reproduction there is the fusion of male and female gamete, they consist of different, genes so during hybridisation offspring may have the variations. In sexual reproduction there is the exchange of genes or crossing over also leads to variations.
These inherited variations increase the survivability of organisms. For example all human beings prior to era originated in Africa, out of them many left Africa and slowly spread over the world. The variation developed by sexual reproduction brought the changes in colour of skin, height, shape etc.
Question 11.
How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer:
Usually in the cells of developed organisms there are two sets of different type of chromosomes, which is shown as 2n and cells are diploid. The genetic materials are situated in these chromosomes. When meiosis take place in reproductive cells of reproductive organs (Testes – male, ovary – female) these mother cells are divided to form gametes which consist haploid n chromosome. During sexual reproduction male and female gamete undergo the fertilisation, then comes the half chromosome from mother (female) and half chromosomes from father (male). In this way the obtained zygote is diploid. The progeny formed from this zygote is having the equal
genetic contribution of male and female parents.
Question 12.
Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Answer:
Yes, the variations that confer an advantage to an individual organism, they presently favourable to environment, then by natural selection they will keep the existence. These variations with time establish in the population in form of chief speciality. Due to these variations organisms is itself adapted to environment and keeps to maintain its progeny continuously in this world.
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